CnChain - CNAME Alias Chains
This module implements incremental alias chains using CNAME (Canonical Name) records. It returns an alias record with an incremented domain name index, forming a chain that continues to increment indefinitely.
Specifically, this module generates a CNAME alias record in the format cnchain###.yourdomain.com
, where ###
represents the incremented index.
The concept is that if the client/resolver attempts to resolve this alias further, it will generate yet another incremented alias, causing the process to continue indefinitely and potentially keeping the resolver occupied.
However, in practice, most modern resolvers detect such chains and terminate the resolution after encountering a certain number of consecutive aliases (e.g., 20 aliases) or upon reaching a specified time limit for the resolution (e.g., 30 seconds).
Note that this feature provides the same functionality as requesting a CNAME record for the generic chain feature.
Category: Alias chains
Tags: Domain Lock-Up, Denial of Service
RFCs: RFC1034
Format
cnchain<NUMBER>.yourdomain.com
Where:
- The
<NUMBER>
parameter specifies an arbitrary number that will be incremented in the response.
Examples
By default, the module generates a CNAME alias with the index of 1:
# dig cnchain.yourdomain.com @127.0.0.1 ; <<>> DiG 9.18.10-2-Debian <<>> cnchain.yourdomain.com @127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43665 ;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;cnchain.yourdomain.com. IN A ;; ANSWER SECTION: cnchain.yourdomain.com. 60 IN CNAME cnchain1.yourdomain.com. ;; Query time: 0 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP) ;; WHEN: Fri Nov 08 23:23:51 +04 2024 ;; MSG SIZE rcvd: 77
If we attempt to resolve the resulting domain name (cnchain1.yourdomain.com
), we receive an incremented alias record:
# dig cnchain1.yourdomain.com @127.0.0.1 ; <<>> DiG 9.18.10-2-Debian <<>> cnchain1.yourdomain.com @127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20108 ;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;cnchain1.yourdomain.com. IN A ;; ANSWER SECTION: cnchain1.yourdomain.com. 60 IN CNAME cnchain2.yourdomain.com. ;; Query time: 0 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP) ;; WHEN: Fri Nov 08 23:23:53 +04 2024 ;; MSG SIZE rcvd: 78
If we continue to resolve the next domain name (cnchain2.yourdomain.com
), we again receive an incremented alias record:
# dig cnchain2.yourdomain.com @127.0.0.1 ; <<>> DiG 9.18.10-2-Debian <<>> cnchain2.yourdomain.com @127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4565 ;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;cnchain2.yourdomain.com. IN A ;; ANSWER SECTION: cnchain2.yourdomain.com. 60 IN CNAME cnchain3.yourdomain.com. ;; Query time: 4 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP) ;; WHEN: Fri Nov 08 23:23:54 +04 2024 ;; MSG SIZE rcvd: 78
This resolution process can continue indefinitely, as there are no limits on the size of the index number. Each resolution yields another incremented alias record:
# dig cnchain9999999999999999999999999.yourdomain.com @127.0.0.1 ; <<>> DiG 9.18.10-2-Debian <<>> cnchain9999999999999999999999999.yourdomain.com @127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62799 ;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;cnchain9999999999999999999999999.yourdomain.com. IN A ;; ANSWER SECTION: cnchain9999999999999999999999999.yourdomain.com. 60 IN CNAME cnchain10000000000000000000000000.yourdomain.com. ;; Query time: 0 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP) ;; WHEN: Fri Nov 08 23:23:55 +04 2024 ;; MSG SIZE rcvd: 127
The domain name will never be fully resolved as the incremental process continues indefinitely.
From the same category
- Chain - Alias Chains
- DnChain - DNAME Alias Chains
- HtChain - HTTPS Alias Chains
- MxChain - MX Alias Chains
- NsChain - NS Alias Chains
- SpfChain - SPF (TXT) Alias Chains
- SrChain - SRV Alias Chains
- SvChain - SVCB Alias Chains